OK, first car I did it on was a 180bhp MSD tuned 2.5V6 Vectra GSI - flat out (think v-max was about 150mph) gave just 5.5 mpg.
That had manifold multipoint sequential injection, and a Bosch ME 3.1.1 engine management. (Very good aerodynamics help to get a got top speed in this).
Next was my former Audi B6 S4 - 4.2 V8 all-alloy engine, 344bhp. V-max was a genuine 162mph, and this gave 6.8 mpg. Again, manifold multipoint sequential injection, with a Bosch ME 7.1 ecu.
And my current Audi B7 RS4 - again with the 4.2 all-alloy V8 engine, but with the 4 valve heads and FSI, and 420bhp. V-max is a genuine 171mph, and this was much better at 9.8mpg.
But the FSI system uses cylinder-direct fuel injectors, fed from a very high pressure 'common rail' fuel line. And as well as them squirting sequentially, they can also multi-pulse per combustion cycle. The ecu is a Bosch MED 9.1, but due to the high revs of the RS4, it actually needs TWO ecus, working on a 'master and slave' principle (both ECUs double up on certain tasks, but certain tasks are specific to either the master module or the slave module).
Finally, all speeds were verified with either one or two GPS units, and the mpg, whilst initially taken from the cars in-built trip computer, was manually verified using old skool calculations.
So, the FSI really does deliver the economy compared to the older manifold injection. My B6 S4 and B7 RS4 are virtually identical aerodynamically (OK, the RS4 is slightly better in front and rear spoiler designs, but then looses out to the S4 with its 'wide' bodyshell, and wider tyres which can notably alter aerodynamics). And weight-wise, they both have a similar kerb weight of 1755 kg, and would have had similar interior loads.
Oh, and the Mk5 GTI also has the same Motronic MED 9.1, but has just one ECU.
